Study On Oil-Water Film Fouling Mechanism Based On Interfacial Microflow Characteristics

The pollution caused by oily wastewater discharged from industry and daily life is endangering the natural environment and human health.Efficient treatment of oily wastewater,especially O/W emulsion in complex environments,is a worldwide challenge.Membrane separation technology is considered to be one of the most effective options for treating emulsified oil.However,in the process of oil-water separation,the membrane is easy to be polluted and the permeability is reduced,which seriously hinders the application and development of membrane separation technology.The essence of membrane fouling is the embodiment of dynamic interface characteristics such as deformation,fragmentation and coalescence of oil droplets on the membrane surface.Therefore,it is of great significance to study the contact angle of oil droplets on the membrane surface and the variation law of dynamic interface in oil-water membrane system.In this paper,the dynamic interface characteristics of emulsified oil droplets on the membrane surface will be studied in detail by combining experimental technologies such as contact angle measuring instrument,high-speed photography and Lattice Boltzmann numerical simulation method.The main work of this paper is as follows:（1）Experiments on the motion characteristics of oil droplets under shear flow and pressure infiltration.The effects of wettability,droplet height and interface tension on the interfacial characteristics of oil droplets are analyzed.The experimental results show that oil droplets are more permeable on the surface of lipophilic membrane.With the increase of the height of oil droplets,the shear drag force of oil droplets increases and the deformation of oil droplets becomes more severe.The decrease of oil-water interface tension will increase the contact angle of oil droplets under water,and oil droplets are more likely to shear slip.（2）Lattice Boltzmann simulation of static pressure infiltration of micro oil droplets.The changes of interface characteristics during the spreading of oil droplets on surfaces with different wettability and the penetration in pores were analyzed.The effects of membrane pore size,Interface tension and pore roughness on the critical penetrate pressure of oil droplets were studied in detail.The simulation results show that the critical penetrate pressure of oil droplets increases with the increase of the ratio of oil droplets size to pore size.The roughness in the pore can increases the critical penetrate pressure of oil droplets,resulting in the residue of oil droplets.With the decrease of effective aperture ratio,the interception rate of oil droplets will gradually increase.（3）Lattice Boltzmann simulation of dynamic infiltration of micro oil droplets.The influence of flow field conditions on the movement of oil droplets is analyzed,and the action mechanism of shear rate,interface tension on the deformation and fragmentation of oil droplets are investigated.The effects of droplet size ratio and bias rate on the coalescence process are further analyzed.The simulation results show that oil droplets have a variety of movement patterns under the action of flow field:fixed above membrane pore,slip,slip and separate from the membrane surface,penetration and neck fracture.Shear flow promotes the tensile deformation of oil droplets along the membrane surface,and the stretching length increases with the increase of shear rate.When the shear rate is high,it will lead to the fragmentation of oil droplets,and the fragmentation rate of oil droplets decreases with the increase of shear rate.The oil droplet size ratio（R₂/R₁）affects the coalescence process of oil droplets.When R₂/R₁<1,the oil droplets cannot coalesce due to the existence of flow dead zone.The oil droplet bias rate also affects the oil droplet coalescence process,and there is a critical bias rateβ_c.When the bias rate is less thanβ_c,oil droplets can coalesce.